Drivetrain issue

2015 Tacoma TRD Off-Road 4WD, 6-speed manual 85K miles
I’ve been chasing a clunk that’s been getting progressively louder and more noticeable. It only happens when there's torque on the drivetrain and I press the clutch in quickly. The clunk feels like a sudden release of load/tension in the drivetrain.

I originally suspected bad transmission or motor mounts, but after reviewing the footage below, they appear to be good (though I’m still somewhat of an amateur).


The clunk happens primarily in first gear under load when I quickly press the clutch — it feels like the drivetrain suddenly unloads. (I can slightly feel the clunk in the car) I also replicated it with the parking brake on: I let the clutch out to the bite point until it shudders, then press it back in — the clunk is audible there too.

It also occurs during rough or poorly matched shifts, especially when downshifting without perfect RPM match.

I’ve checked for engine/transmission movement during these events (see videos), and while there’s some movement, it doesn’t seem extreme — unless I’m underestimating what’s “normal.”

• Clunk test with parking brake on:
• https://youtube.com/shorts/G3SZZOqmF8g?feature=share
  
  
• Clunk noise from undercarriage while driving:
  https://youtube.com/shorts/QRSjIzNOsIw?feature=share

As for diagnosis:

• Motor/trans mounts appear OK visually (see video)
  
  
• I'm wondering (from reading online) if it’s driveshaft slack, U-joints, or possibly differential backlash, but I’m not sure how to confirm. I’d likely have a shop do the actual repair — I just want to have a good idea going in.
  

No recent clutch or transmission work
Any insight from folks who’ve dealt with a similar clunk would be greatly appreciated. I'd like to fix this before it causes more wear or gets worse. Thanks in advance!

 

I would start with checking the ujoints, and center bearing if so equipped.